Recommended Installation Practices

Pre-installing Dependencies

A node host will access the network to install any RPMs dependencies, such as
atomic-openshift-*, iptables, and docker. Pre-installing these
dependencies, creates a more efficient install, because the RPMs are only
accessed when necessary, instead of a number of times per host during the
install.

This is also useful for machines that cannot access the registry for security
purposes.

Ansible Install Optimization

The OpenShift Container Platform install method uses Ansible. Ansible is useful for running
parallel operations, meaning a fast and efficient installation. However, these
can be improved upon with additional tuning options. See the
Configuring
Ansible section for a list of available Ansible configuration options.

Parallel behavior can overwhelm a content source, such as your image registry or
Red Hat Satellite server. Preparing your server’s infrastructure pods and
operating system patches can help prevent this issue.

Run the installer from the lowest-possible latency control node (LAN speeds).
Running over a wide area network (WAN) is not advised, neither is running the
installation over a lossy network connection.

Ansible provides its own
guidance for
performance and scaling, including using RHEL 6.6 or later to ensure the
version of OpenSSH supports ControlPersist, and running the installer from the
same LAN as the cluster, but not running it from a machine in the cluster.

The following is an example Ansible configuration for large cluster installation
and administration that incorporates the recommendations documented by Ansible:

20 forks is ideal, because larger forks can lead to installations failing.

2

Pipelining reduces the number of connections between control and target nodes, helping to improve installer performance.

Networking Considerations

Network subnets can be changed post-install, but with difficulty. It is much
easier to consider the network subnet size prior to installation, because
underestimating the size can create problems with growing clusters.